Generally, in a rewritable optical disk such as DVD-RAM or the like, a recording mark is generated on a track of a disk by power of light to thereby write data. Further, data is read out by utilizing a difference in reflectance of light between the recording mark and a portion outside the mark. In the DVD-RAM, a groove is formed on a disk, and data is written on both the groove and a non-groove portion (land) to attain high density recording.
The control for accurately positioning a head on the track is called tracking. In the DVD-RAM, micro-vibrations of a land and a groove, which are called wobble, are caused, and tracking is performed by utilizing them. When the same data is written in the adjacent tracks, however, the problem encountered is that a tracking signal becomes feeble and tracking tends to slip. In the DVD for processing an image and sound data, frequently the same data such as a silent portions is written in a large amount. To solve this problem, various measures have been taken so that even if a large amount of the same data is written, the written data in the adjacent tracks do not become the same. According to a method disclosed in Japanese Patent Laid-Open No. Hei 6(94)-274885, for example, the beginning of a sector begins at a mark called pit or a non-mark portion called land alternately track by track. Further, according to a method described in ECMA-272 “120 mm Rewritable Disk (DVD-RAM)”, in the DVD-RAM, ID information of each frame is taken as a seed to generate a M-sequence (random sequence), and the M-sequence is added to the user data to be written in a disk. Such data randomizing is generally called scramble.
On the other hand, in field of optical communication, a method called guided scramble has been adopted for the purpose of creating a run-length limited code having a flat frequency characteristic suitable for optical communication. According to this method, data having an enough large space is added to the beginning of the data to create a run-length limited code, thereby producing many kinds of data, and among the data obtained by randomizing the thus produced data, one data near a required characteristic is selected. This method is described in detail in “Codes for Mass Data Storage Systems” K. A. S. Immink, Shannon Foundation Publishers, 1999. Further, as a paper, this method is described in “Polynomials for Guided Scrambling Line Code”, IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, Vol. 13, NO. 3, APRIL. 1995.